Poly(arylene ether) resins are well known and widely used thermoplastics valued for properties including heat resistance, stiffness, and high impact strength. Various methods of preparing poly(arylene ether) homopolymers and copolymers are known, and these materials are often isolated and handled as powders.
U.S. Pat. No. 3,306,875 to Hay generally describes oxidation of phenols to polyphenylene ethers and diphenoquinones. Poly(arylene ether)s prepared include homopolymers of 2,6-dimethylphenol and a copolymer of 2,6-dimethylphenol and 2,6-diethylphenol. Poly(arylene ether)s were typically isolated by combining the polymerization reaction mixture with an anti-solvent, such as methanol, and filtering the resulting precipitate.
U.S. Pat. No. 4,011,200 to Yonemitsu et al. generally describes copolymers comprising 50-98 mole percent of 2,6-dimethylphenol monomer units and 50-2 mole percent 2,3,6-trimethylphenol monomer units. Product poly(arylene ether)s were typically isolated by precipitation and filtration.
U.S. Pat. No. 4,603,1 94 to Mendiratta et al. generally describes a method of isolating polymer resins, including poly(arylene ether)s, from organic solvents. The method comprises volatilizing the organic solvent in the presence of an aqueous slurry of solid polymer particles of a particular size that provides agglomeration sites for the polymer resin within the solution.
U.S. Pat. No. 4,634,761 to Mendiratta et al. generally describes a continuous process for isolating polymer resins, including poly(arylene ether)s, from organic solvents. The process comprises volatilizing the organic solvents in an aqueous solution to form polymer granules, and controlling the size of the granules by interrupting the feed of the organic solvent solution.
U.S. Pat. No. 4,906,700 to Banevicius generally describes a process for reduction of odoriferous poly(arylene ether) by-products, such as 2,3,6-trimethylanisole, by continuously distilling and recycling the aromatic hydrocarbon solvent used in the poly(arylene ether) polymerization. The poly(arylene ether) preparation method described includes a pre-concentration step.
U.S. Pat. No. 6,211,327 B1 to Braat et al. generally describes a process for producing poly(arylene ether) resins having intrinsic viscosities of about 0.08-0.16 deciliters/gram (dL/g) in chloroform at 25xc2x0 C. The poly(arylene ether)s were directly isolated by solvent devolatilization.
European Patent Application No. 153,074 A2 to Kawaki et al. generally describes a process for producing a poly(arylene ether) employing a catalyst composed of a cuprous salt and a primary or secondary amine in a mixed solvent consisting of 1 part by weight of a good solvent for the resulting poly(arylene ether) and 0.9 to 1.1 part by weight of a poor solvent for the resulting poly(arylene ether). The poly(arylene ether) is described as precipitating during the polymerization, and it is isolated by filtration and washing.
European Patent Application 627,466 A2 to Campbell et al. generally describes immiscible polymer blends comprising poly(arylene ether)s having high glass transition temperatures. Example 1 describes the preparation of a poly(arylene ether) copolymer of 2,6-dimethylphenol and 2,3,6-trimethylphenol; the copolymer was isolated by reverse precipitation with acetone and filtration.
Although some of the above methods enable high yields and productivities, the poly(arylene ether) powders they produce may include undesirably high proportions of fines, which are herein defined as solid particles having a particle size less than about 38 micrometers. It is desirable to reduce fines, in that their presence may be associated with losses of the poly(arylene ether) during filtration and drying stages. Other methods may allow the isolation of powders having low content of fines, but they are not readily and economically adaptable to a large-scale manufacturing facility. There remains a need for an economical poly(arylene ether) preparation method that produces poly(arylene ether) powders having a reduced content of fines.
The above-described and other drawbacks and disadvantages of the prior art are alleviated by a method of preparing a poly(arylene ether), comprising: oxidatively coupling a monohydric phenol using an oxygen-containing gas in the presence of a solvent and a complex metal catalyst to produce a poly(arylene ether) resin; removing a portion of the solvent to produce a concentrated solution having a cloud point, Tcloud; and combining the concentrated solution with an anti-solvent to precipitate the poly(arylene ether), wherein the concentrated solution has a temperature of at least about (Tcloudxe2x88x9210xc2x0 C.) immediately before it is combined with the anti-solvent.
In another embodiment, a method of preparing a poly(arylene ether) comprises: oxidatively coupling 2,6-dimethylphenol and 2,3,6-trimethylphenol using an oxygen-containing gas in the presence of toluene and a complex copper catalyst to produce a poly(arylene ether) copolymer resin; removing a portion of the solvent to produce a concentrated solution having a cloud point, Tcloud; and combining the concentrated solution with an anti-solvent to precipitate the poly(arylene ether); wherein the concentrated solution has a temperature, T, immediately before it is combined with the anti-solvent; and wherein T satisfies the inequality   T   greater than       (                                        φ            s                    -                      (                                          0.296                xc3x97                IV                            +                              1.27                xc3x97                TMP                            -              35.7                        )                                    1.97          ⁢                      (                          1              -                              0.00795                xc3x97                IV                            -                              0.0249                xc3x97                TMP                                      )                              -      10        )  
where xc3x8S is the polymer concentration (expressed in weight percent), Tcloud is the cloud point of the system (expressed in xc2x0 C), IV is the intrinsic viscosity of the copolymer in chloroform at 25xc2x0 C. (expressed in mL/g), and TMP is the 2,3,6-trimethylphenol content of the copolymer (expressed in weight %).
Other embodiments, including poly(arylene ether) resins prepared according to the methods, are described below.